1. Field of the Invention
The present invention relates to a method for driving an AC (alternating current) type plasma display panel and more particularly to the method for driving the AC-type plasma display panel which is effective in driving a scanning/sustaining separation three-electrode AC-type plasma display panel.
The present application claims priority of Japanese Patent Application No.2000-110936 filed on Apr. 12, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
Generally, a plasma display panel (hereinafter, referred to as a PDP) incorporates many features in that it can be made thin, it can comparatively easily display a large screen, it can provide a wide-range viewing angle, it can provide a high response speed or a like. Therefore, in recent years, it is used for a wall-mounted television, public display plate or a like in a form of a flat display device. The PDP can be classified, by operation mode, into two groups; one being a DC (direct current)-type PDP adapted to be operated with its electrode being exposed to discharge space (that is, to discharge gas) and in a direct current discharging condition and another being an AC-type PDP adapted to be operated with its electrode coated with dielectric layers and without its electrode being directly exposed to discharging gas and in an alternating current discharging condition. In the DC-type PDP, discharge occurs while a voltage is being applied. In the AC-type PDP, discharge is sustained by changing a polarity of a voltage to be applied. Moreover, in the AC-type PDP, e number of electrodes contained in one cell is two or three.
Configurations and driving method of a conventional three-electrode AC-type PDP are described below. FIG. 7 is a cross-sectional view of one example of a cell used for a conventional PDP. The conventional three-electrode AC-type PDP includes a front substrate 20 and a rear substrate 21 both of which are placed opposite to each other, a plurality of scanning electrodes 22 each being disposed between the front substrate 20 and the rear substrate 21, a plurality of common electrodes 23 and a plurality of data electrodes 29 and display cells (described later in FIG. 8) each being disposed at each of intersections of each of the scanning electrodes 22 and each of the common electrodes 23 and each of the data electrodes 29. As the front substrate 20, a glass substrate or a like is used. Each of the scanning electrodes 22 and each of the common electrodes 23 are placed at a specified interval. On these scanning electrodes 22 and common electrodes 23 is formed a transparent dielectric layer 24. On the transparent dielectric layer 24 is formed a protecting layer 25 made up of MgO (Magnesium oxide) or a like adapted to protect the transparent dielectric layer 24 from discharging. On the other hand, as the rear substrate 21, a glass substrate or a like is used. Each of the data electrodes 29 is so mounted as to be orthogonal to each of the scanning electrodes 22 and to each of the common electrodes 23. On the data electrodes 29 is formed a white dielectric layer 28. On the white dielectric layer 28 is formed a phosphor layer 27. Between front substrate 20 and rear substrate 21 is placed a partition wall (not shown) at a specified interval in parallel to a face of paper in which FIG. 7 is shown. The partition wall is used to secure discharge space 26 and to demarcate pixels. The discharge space 26 is filled, in a sealed manner, with mixed gas such as He (Helium), Ne (Neon), Xe (Xenon) or a like, as discharge gas to be used for discharge. The conventional three-electrode AC-type PDP having such configurations as described above is disclosed in SID (Society for Information Display) 98 DIGEST (P279-281, May, 1998).
FIG. 8 is a plan view of the conventional three-electrode AC-type PDP. As shown in FIG. 8, at each of intersections of each electrode Si (i=1 to m) making up the scanning electrodes 22 and each electrode Ci (i=1 to m) making up the common electrode 23 and each electrode Dj (1 to n) making up the data electrode 29, each of display cells 31 is disposed. These display cells 31 are placed in a matrix form.
Next, a conventional method for driving a PDP will be described below. As the method for driving the PDP, a scanning/substaining separation method (ADS method) in which a scanning period and a sustaining period are separated is in the present mainstream. However, this method requires a plurality of sub-fields (SF) for displaying a gray shade and also requires the scanning period for each of the SFs. Therefore, if the number of gray scales or the number of scanning lines is increased, the scanning period forms an increasing proportion of one field and, as a result, the sustaining period forms a decreasing proportion of the one field, causing low luminance in display. To solve this problem, an alternative method for driving the PDP by which the gray shade can be displayed by one time scanning without using such SFs is proposed. The method of this type for driving the PDP is disclosed, for example, in Japanese Patent Application Laid-open No. Hei 9-81073.
The scanning/sustaining separation method will be described. FIG. 6 is a diagram showing waveforms explaining driving operations of the conventional three-electrode AC-type PDP. One field 1 is made up of three periods including a preliminary discharge period 2, a scanning period 3 and a sustaining period 4.
First, the preliminary discharge period 2 will be described. A preliminary discharge pulse 5 with positive polarity is applied to the common electrode 23 and a preliminary discharge pulse 6 with negative polarity is applied to the scanning electrode 22. This enables resetting of irregularity caused by light emitting conditions in a pre-field period, in a state in which wall charges occur at a final stage of a pre-SF and enables initialization and, at a same time, this causes all pixels to be forcedly discharged, thus providing a priming effect which induces subsequent writing discharge to occur at a lower voltage. Since this preliminary discharge pulse 5 causes all pixels to be discharged, a voltage of the preliminary discharge pulse 5 has to be higher than those of a scanning pulse and sustaining pulse.
Moreover, though, in the example shown in FIG. 6, both the preliminary discharge pulses 5 and 6 are applied once with same timing, in some cases, two kinds of pulses each having a different role are applied, that is, a priming pulse to cause all pixels to be discharged and priming effects to be implemented is applied after a sustainment extinguishing pulse to cause the state of the pre-field to be reset has been applied. At this point, in some cases, a different sustainment extinguishing pulse is applied not only once but also two or more numbers of times.
Furthermore, though, in the example shown in FIG. 6, to extinguish the wall charge produced by the preliminary discharge, a self-extinguishing process by using a fall of each of the preliminary discharge pulses 5 and 6 is employed, in some cases, a preliminary discharge extinguishing pulse is applied to extinguish these wall charges separately. In some cases, the preliminary discharge extinguishing pulse is also applied not only once but also two or more numbers of times.
Moreover, in some cases, these pulses are applied to other electrodes. In any case, the wall charge on the dielectric layer produced by the preliminary discharge is extinguished or is controlled to be proper in quantity.
Next, the scanning period 3 is described below. During the scanning period 3, the scanning pulse 8 is applied sequentially to each of electrodes (S1 to Sm) making up the scanning electrode 22. At the same time when the scanning pulse 8 is applied, a data pulse 9 is applied, in a manner so as to correspond to a display pattern, to each of electrodes (D1 to Dm) making up the data electrode 29. The data pulse 9 changes a pulse voltage in a manner depending on gray scale to be displayed. In the case of a gray scale with low luminance, the pulse voltage is set to a low level and, then, the voltage is boosted as luminance becomes higher. When application of the scanning pulse 8 is completed, a wall charge being almost equivalent to a potential difference between the scanning pulse 8 and the data pulse 9 is accumulated by writing discharge. Therefore, a large amount of the wall charge is accumulated in a pixel into which a signal with high luminance has been input and a small amount of the wall charge is accumulated in the pixel into which a signal with low luminance has been input. A scanning base voltage 7 being applied to the scanning electrode 22 during the scanning period is applied to prevent erroneous discharging that may occur, after the writing discharge, between the scanning electrode 22 and the common electrode 23 of a pixel being adjacent to the scanning electrode 22 (that is, between non-discharging gaps).
After the scanning pulse 8 has been applied to all lines, a sustaining period 4 starts. Each of the sustaining pulses 10 and 11 is applied alternately to all of the scanning electrodes 22 and all of the common electrodes 23. Voltages of the sustaining pulses 10 and 11 are increased in stages during the sustaining period. As a result, potential difference between the scanning electrode 22 and the common electrode 23 increases as their polarities are reversed. However, this voltage is set to a level at which discharge does not occur. Therefore, since an amount of the wall charge is small in a pixel in which writing discharge has not occurred, even when the sustaining pulses 10 and 11 are applied, no discharge occurs.
On the other hand, in the pixel in which the writing discharge occurs, the wall charge is accumulated in a manner to correspond to a gray shade. During the sustaining period 4, a voltage resulting from superposition of a voltage produced by the wall charge accumulated in the scanning electrode 22 by the writing discharge on the potential difference between the sustaining pulses 10 and 11 is applied between the scanning electrode 22 and the common electrode 23. Since the sustaining pulse voltage is increased in stages, when it exceeds a start voltage for surface discharge at some point in time, the surface discharge occurs between the scanning electrode 22 and the common electrode 23. At this time, since a data base voltage 12 is applied to the data electrode 29, no opposite discharge occurs. The xe2x80x9copposite dischargexe2x80x9d here refers to the discharge which occurs between electrodes placed opposite to each other.
Once the surface discharge occurs, a large amount of the wall charge with reverse polarity is accumulated in the scanning electrode 22 and the common electrode 23. The accumulated wall charge, since the subsequent sustaining pulse voltage with reverse polarity is superposed on the wall charge, produces a large potential difference, thus causing the surface discharge with reverse polarity to occur again and a large amount of the wall charge with reverse polarity to be again accumulated. Thus, once the surface discharge occurs, every time the polarity of the sustaining pulse is reversed, the surface discharge is repeated until the sustaining period 4 ends.
A timing of a start of the surface discharge changes depending on an amount of the wall charge accumulated by the writing discharge. That is, if the amount of the wall charge is small, the sustaining pulse with a high voltage is required and the surface discharge does not start until the sustaining pulse 11 with the high voltage produced at a later stage of the sustaining period 4 is applied, while, if the amount of the wall charge is large, the surface discharge starts when the sustaining pulse with a low voltage is applied. Thus, by changing a period while light is emitted (that is, the period while discharge occurs) during the sustaining period 4 depending on the amount of the wall charge, the number of discharge is changed. Since the wall charge is produced by the writing discharge depending on the gray scale to be displayed, the number of the discharge can be controlled depending on the gray scale. Thus, the display of the gray scale is implemented by controlling number of times of the discharge.
As described above, while the writing discharge occurs, the wall charge is produced in the scanning electrode 22 by the opposite discharge. During the sustaining period 4, a voltage produced by the wall charge is superposed on the voltage of the sustaining pulse and, when the superposed voltage exceeds a start voltage for the discharge, the surface discharge occurs. In the case of the surface discharge, since the discharge starts in the proximity of a gap area for the surface discharge, that is, at an edge area where the scanning electrode 22 and the common electrode 23 are placed, in a same pixel, opposite to each other, the discharge cannot be stable because the discharge occurs at such a small end area on a line, thus causing flicker which occurs for a while even after the sustaining voltage has been boosted.
FIG. 9 is a diagram showing a relationship between a data pulse voltage and a start voltage for the discharge at which the surface discharge starts, obtained when driving the conventional three-electrode AC-type PDP by using the conventional driving waveforms as shown in FIG. 6. As shown in FIG. 9, the star voltage for the surface discharge varies linearly with the data pulse voltage. However, an unstable region 42 in which the discharge is unstable, causing flicker in display, exists between a discharging area 40 and a non-discharging area 41. In order to prevent such flicker from occurring during the sustaining period, as shown by a dashed line in FIG. 9, it is necessary to set both the data pulse voltage and sustaining pulse voltage at discrete values. At this point, the increased unstable region 42 causes a decrease in the number of gray scales that can be set.
Alternatively, it is possible to display gray scales even by using a method in which the sustaining pulse voltage is continuously increased. However, the increased unstable region 42 also causes flicker in displaying to be perceived by an eye, which is regarded as deterioration in displaying performance. When a low gray scale is displayed, in particular, a flickering period forms a large proportion in light-emitting periods, which is regarded as remarkable deterioration.
In view of the above, it is an object of the present invention to provide a method for driving an AC plasma display panel which makes it possible to reduce an unstable period of discharging, thus enabling an increased number of gray scales in display and reduction of flicker.
According to a first aspect of the present invention, there is provided a method for driving an AC-type plasma display panel wherein scanning electrodes and common electrodes are mounted on one of two insulating substrates placed opposite to each other and data electrodes are mounted on the other of the two insulating substrates in a manner so as to be orthogonal to both the scanning electrodes and the common electrodes, and pixels are formed at intersections of the scanning electrodes and the data electrodes in a matrix form, wherein operations are performed during a scanning period when a scanning pulse and a data pulse to cause writing discharge producing wall charges to occur so as to correspond to gray shades to be displayed, are applied sequentially to the scanning electrodes and the data electrodes and during a sustaining period when a sustaining pulse is applied alternately to each of the scanning electrodes and the common electrodes to cause sustaining discharge to occur which induces light emitting for displaying and wherein a number a the wall charge produced during the scanning period, the method including:
a step of controlling the number of times of the sustaining discharge by changing timing when the sustaining discharge starts according to amounts of the wall charge during the sustaining period, wherein the discharge occurring with timing when the sustaining discharge starts is an opposite discharge which occurs between the scanning electrodes and the data electrodes.
With the above configuration, a potential between the scanning electrode and the common electrode is set so that the discharge occurring when the sustaining discharge starts is the opposite discharge between the scanning electrode and the data electrode. Though a discharge between the scanning electrode and the common electrode is induced by the opposite discharge concomitantly, timing when the sustaining discharge starts is decided by a potential difference between the electrodes placed opposite to each other.
According to a second aspect of the present invention, there is provided a method for driving an AC-type plasma display panel wherein scanning electrodes and common electrodes are mounted on one of two insulating substrates placed opposite to each other and data electrodes are mounted on the other of the two insulating substrates in a manner so as to be orthogonal to both the scanning electrodes and the common electrodes, and pixels are formed at intersections of the scanning electrodes and the data electrodes in a matrix form, wherein operations are performed during a scanning period when a scanning pulse and a data pulse to cause writing discharge producing wall charges to occur so as to correspond to gray shades to be displayed, are applied sequentially to the scanning electrodes and the data electrodes and during a sustaining period when a sustaining pulse is applied alternately to each of the scanning electrodes and the common electrodes to cause sustaining discharge to occur which induces light emitting for displaying and wherein a number of times of the sustaining discharge is controlled by amounts of the wall charge produced during the scanning period, the method including:
a step of controlling the number of times of the sustaining discharge by changing timing when the sustaining discharge starts according to amounts of the wall charge during the sustaining period;
a step of controlling timing when the sustaining discharge starts according to a potential difference between each of the scanning electrodes and each of the data electrodes; and
wherein surface discharge occurs at each of the scanning electrodes and each of the common electrodes after opposite discharge between each of the scanning electrodes and each of the data electrodes has occurred.
In the foregoing, a preferable mode is one wherein, when a gray level signal having maximum luminance is input, a potential difference between each of the scanning electrodes and each of the data electrodes is set so that sustaining discharge occurs between each of the scanning electrodes and each of the data electrodes by the sustaining pulse to be produced at an initial stage of the sustaining period.
Also, a preferable mode is one wherein the amount of the wall charge varies depending on a potential difference between the scanning pulse and the data pulse which are produced so as to correspond to luminance and gray levels.
Also, a preferable mode is one wherein, when a gray level signal having minimum luminance is input, a potential difference between each of the scanning electrodes and each of the data electrodes is set so that no discharge occurs between each of the scanning electrode and each of the data electrodes during the sustaining period.
Also, a preferable mode is one wherein a potential difference produced when the sustaining discharge starts increases gradually during the sustaining period.
Also, a preferable mode is one wherein a pulse whose polarity being opposite to that of the scanning pulse is applied when the sustaining discharge starts.
Also, a preferable mode is one wherein a voltage of the scanning pulse is negative.
Also, a preferable mode is one wherein a potential difference between each of the scanning electrodes and each of the data electrodes, which is produced when the sustaining discharge starts, is increased gradually, during the sustaining period, by changing a potential of the data electrode.
Also, a preferable mode is one wherein a potential difference between each of the scanning electrodes and each of the data electrodes, which is produced when the sustaining discharge starts, is increased gradually, during the sustaining period, by continuously changing a potential of the data electrode.
Also, a preferable mode is one wherein a potential difference between each of the scanning electrodes and each of the data electrodes, which is produced when the sustaining discharge starts, is increased gradually, during the sustaining period, by changing, in stages, a potential of the data electrode.
Also, a preferable mode is one wherein the potential of the data electrode to be changed in stages is made equal to the potential of the data pulse to be applied during the scanning period.
With the above configuration, the number of voltages to be set for a data driver can be reduced.
Also, a preferable mode is one wherein each of the preliminary discharge period, the scanning period and the sustaining period is defined as one sub-field and a plurality of the sub-fields make up one field to display one screen.
Also, a preferable mode is one wherein each of the sustaining periods making up the one sub-field within the one field has sustaining pulses in different number.
With the above configuration, the number of gray scales can be increased.
Furthermore, a preferable mode is one wherein all of the number of the sustaining pulses in each of the sub-fields in the one field during a period from a start of the sustaining discharge to an end of the sustaining period, is different in the one field.
With the above configurations, the display of gray shades is implemented by changing the timing when the sustaining discharge starts so as to correspond to the wall charges accumulated by writing discharge and the discharge occurring when the sustaining discharge is started can be made stable and, when same gray shades are displayed, the discharge can be started with the exactly same timing to perform the display of the same gray shades.